Understanding the onset of Alzheimer's disease (AD) requires the development of new research methods, which can be applied to preclinical disease and for the generation of new as well as the improvement of currently available drugs such as those which augment cholinergic neurotransmission early in the progression of AD. During the current five years of the PPG, subproject 2 has pioneered methods for using liquid chromatography coupled with tandem mass spectrometry for proteomic examination of brain tissue to study the proteome of AD during disease progression. These efforts led to the discovery of pathological accumulations of components of the Ul small nuclear ribonucleoprotein (Ul snRNP) and global disruption of RNA processing in Alzheimer's disease (AD). We will apply these innovative proteomics approaches along with well-established biochemical and immuohistochemical methods to 1) define pathological accumulations of Ul snRNP within the cortical regions which compose the memory default network which receive extensive cholinergic innervation from the long cortical cholinergic projection neurons located within the subfields of the nucleus basalis of Meynert during progression of AD, 2) Identify changes in Ul snRNP components, posttranslational modifications of tau, and novel proteins that define cholinergic basal forebrain neuron subfield dysfunction that follows a caudal to rostral progression the during progression of AD, and 3) examine changes In RNA processing linked to Ul snRNP pathology within the cholinergic basal forebrain neurons during the progression of AD. The proposed studies will improve our understanding ofthe role of Ul snRNP in the development and progression of AD, and likely to identify novel mediators of disease. Such advances are critical to advancing our understanding of AD and the development of more effective therapeutics.